Currently I’m using booky mcbookface but the app is really lacking and the scrolling is not smooth.
Edit: I came across Lithium and Readera which both don’t seem to collect much information compared to other apps. Not sure if they’re open source though.
KOReader on my old Tolino with Android.
It’s not beautiful but full of features and you can configure everything. I can directly download the books from my Calibre Web Automated container via opds.